P1,P4-di(uridine 5′-)tetraphosphate (hereinafter written as “UP4U”) represented by the following formula [I] or a salt thereof is used as a therapeutic drug for keratoconjunctive epithelium disorder accompanying dry eye, and is also a compound having an expectoration-inducing effect and thus is envisaged to be developed as an expectorant or a therapeutic drug for pneumonia.
Conventionally, as a method for synthesizing UP4U, there have been reported a method of reacting uridine 5′-cyclic triphosphoric acid prepared by dehydration condensation of uridine 5′-triphosphoric acid (UTP) with uridine 5′-monophosphoric acid (UMP) (Non Patent Document 1) and an improved method thereof (Patent Document 1).
